Lightlike Submanifolds of a Para-Sasakian Manifold

In the present paper we study lightlike submanifolds of almost paracontact metric manifolds. We de ne invariant lightlike submanifolds. We study radical transversal lightlike submanifolds of para-Sasakian manifolds and investigate the geometry of distributions. Also we introduce a general notion of paracontact Cauchy-Riemann (CR) lightlike submanifolds and we derive some necessary and su cient conditions for integrability of various distributions of paracontact CR-lightlike submanifold of a para-Sasakian manifold.